copper rove size for rudder head/blade join?

[Thorne]

I was going to attach the two oak cheekpieces to the blade of the kickup rudder with copper rove rivets, but am unsure of the size to use -- haven't used that type of fastener before. Can't find bronze plate at an affordable price, and want the rudder to have all bronze hardware.

http://www.luckhardt.com/rudderplan1sm.jpg

The oak pieces will be roughly 7/8" - 3/4" thick each, so combined with the width of the blade at 7/8", the length of the copper nails needs to be at least 3 inches.

No problem with getting them a bit long since they are nipped off anyway, but Jamestown sure gets a lot for the longer ones!

Another fastener question - I was planning on using either a 5/16" or 3/8" bronze carriage bolt for the pivot pin, with bronze washers and hex nut. Will a 3' rudder blade weighted with lead require a larger bolt like 1/2"?

Any suggestions for size and source? Jamestown is easy to order from, but not the cheapest usually.

http://www.jamestowndistri butors.com/find;a;1;ID;,Fasteners,Nails,Rose.Head.Copper.Nail s (http://www.jamestowndistributors.com/find;a;1;ID;,Fasteners,Nails,Rose.Head.Copper.Nail s)

[ 12-15-2005, 08:55 AM: Message edited by: Thorne ]

[Jay Greer]

So far as the bronze bolt is concerned, I would make it out of bronze rod, available from a local supplier as well as Seattle Brass. Threading the rod and nutting both ends should do the trick and assure that a seal can be applied to both sides, which is not the case with a carriage bolt. I would lock peen punch the nut on one end and use flax and tallow impregnated washers to seal them under a bronze washer on both sides. This may seem archaic but it is still the best way to seal a center board pivot pin bolt. The roves and nails are also available from the Wooden Boat Foundation in Port Townsend WA.
Opps, I just re-read and saw that this is a question concerning a rudder pivot bolt. Anyway, the sources are the same and the materials still will do. However, a carriage bolt wil work and I would put the tallow and flax washers with in the faying surfaces.
JG.

[ 12-14-2005, 01:36 AM: Message edited by: Jay Greer ]

[Thorne]

Jay -

Thanks! Yes, it DID seem a bit excessive to work at sealing a rudder pin like that...

;- )

Question on the copper rove rivets -- Jamestown only offers one size (13G) at that length, and the longest on offer was 2" (12G). Does this mean that this type of fastener isn't good at these lengths? Should I get the 2" 12G size for extra strength?

Also if the rudder kicks up suddenly, it will transfer some of that energy to the cheekpiece fasteners. I plan on using 6-8 of them, but does the fact that they are dealing with some shear force mean that I should use stronger fasteners, possibly bronze bolts?

[ 12-14-2005, 08:33 AM: Message edited by: Thorne ]

[GregH]

Thorne-

Regarding your question about the size of the pivot bolt-
When teaching metallurgy years ago, I would demonstrate to my classes various mechanical properties of various metals. Although we never used bronze, brass rods were regularly used, putting them in compression, tension and shear. From your drawing, it appears that the primary load on the pivot bolt is shear (although it is rare that ANY structural member in ANY structure is subject to a single force). The cheeks taking the real (lateral) force on the rudder. So the bolt appears for the most part, to only bear the weight of the blade.
The brass samples usually exhibited a shear strength of something in the neighborhood of 30k to 35k psi. Not knowing exactly the grade or alloys involed, lets assume your bronze is at least equal to the my brass (there has to be a joke in there somewhere!). At 30k psi, a 5/16" bolt has an actual shear strength over 3300 pounds! Even a 1/4" bolt comes in at just under 1500 lbs. How much does does this blade weigh??

[GregH]

Thorne-

Regarding your question about the size of the pivot bolt-
When teaching metallurgy years ago, I would demonstrate to my classes various mechanical properties of various metals. Although we never used bronze, brass rods were regularly used, putting them in compression, tension and shear. From your drawing, it appears that the primary load on the pivot bolt is shear (although it is rare that ANY structural member in ANY structure is subject to a single force). The cheeks taking the real (lateral) force on the rudder. So the bolt appears for the most part, to only bear the weight of the blade.
The brass samples usually exhibited a shear strength of something in the neighborhood of 30k to 35k psi. Not knowing exactly the grade or alloys involed, lets assume your bronze is at least equal to the my brass (there has to be a joke in there somewhere!). At 30k psi, a 5/16" bolt has an actual shear strength over 3300 pounds! Even a 1/4" bolt comes in at just under 1500 lbs. How much does does this blade weigh??

[ 12-14-2005, 09:12 AM: Message edited by: GregH ]

[Thorne]

Greg -

Thanks for the reply. Rudder blade only weighs about 7 pounds or so, but I'm concerned about bending as well as shear. If the pivot bolt bends enough, it will cause the rudder to not work...always a problem.

Actually I'm more concerned about the copper rove rivets, but I'll guess that with that many, shear isn't really an issue. And I can always use epoxy or Vulkem 116 or PL Premium to glue the cheekpieces to the rudder blade, giving additional strength to the attachment situation.

I'll probably go for the larger diameter copper nails and just trim the length, although the price nearly doubles.

[ 12-14-2005, 10:10 AM: Message edited by: Thorne ]

[GregH]

Thorne-

There shouldn't/won't be any lateral torsional loads on the bolts( those being abosrbed by the cheeks), so bending should not be a concern. There might be some eventual deformation of the holes in the wooden pieces, butsince they're oak, it should not be a factor. If this is still a concern, the holes can be bushed. But then, that's a lot of extra work and complexity, so you could just throw in a larger bolt to expand the surface area in the holes, but then again, your're back to square one!! Design and engineering are always a matter of compromise- just be thankful that you're not trying to produce this commercially, trying to keep costs down, etc. etc.!!!

[Thorne]

Well, the wife is doing the cost control bit already..."Do you know how much you've spent on that boat so far?"

;- z

Just ordered the copper nails, roves, and various bronze bits from Hamilton in time for Christmas delivery...wheee!

[ 12-14-2005, 05:05 PM: Message edited by: Thorne ]

[Steve Lansdowne]

You ARE going to name the boat after your wife, right?

[Bob Cleek]

Well, since you already ordered them, this is a day late and a dollar short. Roves and rod aren't rocket science. If the problem arises again, simply use copper rod and any old copper you can find for a rove. While it pays to use nails and roves when planking and such, for larger, odd sized tasks, you can easily make your own. A quarter inch copper rod, peened on one end in the vise, with a drilled penny on either end would work fine for your rudder stock faces.

[Thorne]

Bob -

Thanks for the input, I'll remember it for later applications.

I know that wooden boats are expensive, but isn't using coins as fastener parts sort of rubbing it in?

;0 )

[ssor]

I drilled a handful of nickels to make buttons for a project. Cheaper than store bought and stronger.